Solid free-form fabrication (SFF) is a designation for a group of processes that produce three dimensional shapes from additive formation steps. SFF does not implement any part-specific tooling. Instead, a three dimensional component is often produced from a graphical representation devised using computer-aided modeling (CAM). This computer representation may be, for example, a layer-by-layer slicing of the component shape into consecutive two dimensional layers, which can then be fed to control equipment to fabricate the part. Alternatively, the manufacturing process may be user controlled instead of computer controlled. Generally speaking, a component may be manufactured using SFF by successively building feedstock layers representing successive cross-sectional component slices. Although there are numerous SFF systems that use different components and feedstock materials to build a component, SFF systems can be broadly described as having an automated platform/positioner for receiving and supporting the feedstock layers during the manufacturing process, a feedstock supplying apparatus that directs the feedstock material to a predetermined region to build the feedstock layers, and an energy source directed toward the predetermined region. The energy from the energy source modifies the feedstock in a layer-by-layer fashion in the predetermined region to thereby manufacture the component as the successive layers are built onto each other.
One recent implementation of SFF is generally referred to as ion fusion formation (IFF). With IFF, a torch such as a plasma, gas tungsten arc, plasma arc welding, or other torch with a variable orifice is incorporated in conjunction with a stock feeding mechanism to direct molten feedstock to a targeted surface such as a base substrate or an in-process structure of previously-deposited feedstock. A component is built using IFF by applying small amounts of molten material only where needed in a plurality of deposition steps, resulting in net-shape or near-net-shape parts without the use of machining; molds, or mandrels. The deposition steps are typically performed in a layer-by-layer fashion wherein slices are taken through a three dimensional electronic model by a computer program. A positioner then directs the molten feedstock across each layer at a prescribed thickness.
One inherent challenge when building a component using an IFF process is establishing and maintaining a heat balance between the weld pool, the torch, and the substrate. IFF enables fabrication of nearly any net shape using metals, ceramics, or plastics as feedstock by controlling the freezing rate of the molten material. Liquid feedstock and/or substrate may flow away instead of providing additionally built-up structure if the weld pool does not quickly solidify. The molten continuous stream, or each molten droplet in a discontinuous stream, will add incremental shape for building a final component if solidification quickly occurs when the stream contacts the underlying substrate or component material.
Hence, there is a need for an IFF process that include a technique for improving heat input to the molten feedstock and/or temperature of the underlying component material when heated feedstock is deposited onto a targeted surface to build the component. There is a further need for a technique that can be implemented without adding major components to existing IFF systems.